This invention relates to compressors, to positive-displacement compressors, and to double-acting piston compressors. The invention is directed more specifically to such a compressor having a pair of parallel, double-headed pistons reciprocably mounted in a common housing or cylinder block. The compressor according to the invention finds use, for example, as a refrigerant compressor in an automotive air conditioning system.
U.S. Pat. No. 3,797,969, issued to Weatherhead et al. on Mar. 19, 1974, describes and claims a refrigerant compressor of the double-acting piston type herein under consideration. The compressor comprises a pair of double-headed pistons reciprocably fitted in respective cylinder chambers defined by a common housing. A crankshaft extending transversely through the cylinder chambers has a pair of offset cranks, one for each piston, on which there are mounted Scotch-yoke-type sliders slidably fitted in transverse passages or tracks in the respective pistons. The sliders function to transform the rotation of the crankshaft into rectilinear reciprocation of the pistons.
Each slider used in such a double-acting piston cylinder is usually more or less rectangular in shape, having a bore, complete with a bushing or equivalent means, extending centrally therethrough. At least two opposite surfaces of the slider are parallel for sliding contact with one of the pistons. The sliders are referred to as the unitary type, in contradistinction to a split type.
The configuration of a double-acting piston compressor with such unitary sliders depends in no small measure upon the manner in which the sliders are mounted in position during the assemblage of the compressor. The sliders must rotatably fit over the cranks of the crankshaft and further must be slidably received in the transverse passages in the pistons for linear reciprocation. All these sliders, crankshaft and pistons, moreover, must be operably mounted within the compressor housing. Thus the manner of assemblage of the compressor not only determines its size and weight but also materially affects the machinability of its parts and the durability of the apparatus. A more detailed discussion of problems involved in compressor configuration and assemblage follows.
The mounting of the unitary sliders on the cranks has heretofore required that the cranks be considerably larger in diameter than the other crankshaft portions. Such large diameter cranks necessitate the use of sliders having bores of correspondingly great diameter so that the sliders may pass over the end portions of the crankshaft onto its crank. The crankshaft portions other than the cranks should not be made unduly slender, however. For the crankshaft with such slender portions would deflect during compressor operation, thus giving rise to mechanical vibration, noise, and rapid wear of sliding parts.
Should the cranks be of excessively great diameter, on the other hand, the external size of the sliders would increase correspondingly. Such large sliders would not be mounted in position without a corresponding increase in the spacing between the side columns joining the opposed heads of each piston. Since the pistons as a whole should preferably be of generally cylindrical shape, however, the increase in the spacing between the side columns would demand a decrease in their thickness and, therefore, strength if the piston diameter was to remain unchanged.
Several other approaches have been suggested for mounting the unitary sliders in position. Such known approaches include:
1. To make detachable two of the four side columns of each piston, thereby making it possible to move the sliders into the pistons without decreasing the thickness of the columns.
2. To split each piston into halves along a plane perpendicular to its axis.
3. To increase the axial length of each piston and to make the side columns project beyond the diameter of the piston heads, thereby making possible the mounting of the sliders and further increasing the strength of the side columns.
All these conventional approaches have one or more of such drawbacks as lower machinability of the required parts, less precision with which the parts are assembled, and greater bulk of the resulting compressor.
Another known slider mounting method calls for the splitting of the crankshaft into cranks and other shaft portions. This method not only makes it easy to mount the sliders in position but also permits reduction of the crank diameter to a minimum, resulting in the provision of a compact compressor. These advantages are offset, however, by the lower rigidity and less accurate dimensions of the assembled crankshaft. The durability of a compressor with such a split crankshaft is also questionable.
The foregoing study of the prior art will have made clear that if the double-acting piston compressor of the type under consideration is to employ unitary sliders, at least either of the housing, pistons, and crankshaft has had to be of the split type in order to keep the size of the compressor at a desired minimum. The use of such split parts involves the noted problems in strength and accuracy of dimensions.